Boeseman’s rainbowfish



The Boeseman’s rainbowfish is a small and colorful fish living in only a few freshwater lakes and rivers in New Guinea. As with most fish in these lakes, they live in the shallows where prey is more abundant. These schooling fish have very brightly-colored males and much duller females.  The males are a blue to gray color on the front half of their body while the back half is a bright orange-red. The males also have some greenish stripes where the two main colors meet. In the picture above, they are harder to see, but you may be able to find two vertical whitish-green stripes there. These rainbowfish have two dorsal fins: a smaller one about halfway across their body and a longer one that runs from slightly after this one to the tail fin. The latter one lacks spines while the other one does not. The dorsal fins of females are smaller than those of males.  This fish was named after Marinus Boeseman, a Dutch ichthyologist in the 20th century.


This species of rainbowfish can grow up to six inches (15 cm) long, although they normally stay only around four inches (10 cm) long. Males are slightly larger than females. This is part of the reason females have a smaller dorsal fin than males, but these fins are also smaller proportionately.


Boeseman’s rainbowfish, as with most rainbowfish, are omnivores, eating plants and animals. Some of their meals include algae, aquatic insects, and even some small crustaceans. Their diet gives them their bright colors.


Like most fish, Boeseman’s rainbowfish spawn in order to reproduce. This procedure can occur year round or can come with the rainy season. The eggs are laid among aquatic plants. In aquariums, up to twenty eggs are laid each day. These eggs hatch after around two weeks, depending on the water temperature.

In aquariums

Boeseman’s rainbowfish are often kept in aquariums, their bright colors making them an attractive fish to keep. Since they are tropical fish, these animals like warm water that is normally in between 79 and 86 degrees Fahrenheit (26-30 degrees Celsius). The water should have a PH level of a least 7.0 and a hardness level of around 5 gDH. In aquariums, they should be kept in groups of no less than six, but preferably even more. Because their habitat is heavily planted, they would like any other home to be the same. Since they have almost unlimited space in their natural home, aquariums housing these animals should be at least thirty gallons (114 litres). If breeding is desired in aquariums, a slight raise of temperature may help induce spawning. It is suggested to move eggs and young to a different tank in order to make them easier to raise. They are not aggressive and also do not harm plants, which is good news for aquarium owners wanting this species.


Due to their popularity in  aquariums, the wild population of Boeseman’s rainbowfish declined rapidly in the 1980’s with up to 60,000 males being exported each month. The government where these animals live has now restricted trade of them and now most pet rainbowfish are raised in captivity. This species is listed as “Endangered” in the IUCN Red List of Threatened Species.

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Photo credits:

  • Boeseman’s rainbowfish – Rosaringazo
  • Mystery animal – Thomas Brown

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